RAID users can generally configure a virtual disk in either write back or write through policy. Write through policy guarantees data integrity. Write back cache policy provides superior I/O throughput.
A RAID controller card may have a battery or a Supercap solution for disk failures. A battery/supercap solution can hold data (pinned cache) present in memory for a certain time period when a server does not have a power supply. When pinned cache data is present, cache lines are used to store pinned Cache and all other online virtual disks will operate in write through mode until either pinned cache is discarded or missing virtual disks are imported back to recover pinned cache through flushing.